Diode-triode apparatus



Aug. 19, 1941; I LACEY 2,253,337

DIODE-TRIODE APPARATUS Filed June 1, 1940 INVENTOR E. LACE) A TTORNEV Patented Aug. 19, 1941 DIODE-TRIODE APPARATUS Edwarrl Lacey; Schenectady,..N. Y., assignor to Bell Telephone Laboratories, Incorporated,

New York, a corporation of New York Application June 1, 1940, Serial No. 338,311

3 Claims.

triode amplifier included in diode-triode apparatus known heretofore, a resistance embodied in the filament circuit may serve to produce a biasing voltage for the control grid of the triode.

' One difiiculty with such arrangement is that a biasing voltage of the same order of magnitude is also simultaneously applied to the diode. Consequently, no rectified current may flow until the peaks of the input signaling voltage overcome the negative bias on the diode. This tends to limit the sensitivity of the diode-triode apparatus and to change the rectified current-input characteristic thereof. Accordingly, this invention contemplates a diode-triode circuit organization which enables the application of a suitable biasing voltage to the control grid of the triode while at the same time maintaining zero bias on the diode.

The general object of the invention is to bias the control grid of a triode in a manner which is independent of the diode.

Another object is to increas the sensitivity of diode-cathode apparatus.

A common type of diode-triode apparatus embodies in a single envelope a diode and a triode, and utilizes a direct current source to energize the cathode heater thereof.

In a preferred embodiment, the invention comprises a bridge network having one diagonal connested in series in the diode circuit and an opposite diagonal connected in series in the circuit embodying the cathode heater source. A variable connection from the network to the control grid of the triode serves to supply thereto a negative biasing vltage of suitable magnitude.

A feature of this arrangement is that the diode circuit is maintained substantially at zero bias, that is, the shape of the rectified current-alternating current input characteristic is substantially unaffected by the bias applied to the triode amplifier. A further feature is that such biasing arrangement is achieved without the necessity of using a separate C battery.

The invention will be readily understood from the following description taken together with the accompanying drawing the single figur of which is a schematic circuit diagram of a preferred form of the invention. I

Referring to this drawing, input circuit IIJ,

iii

adapted to be connected to any suitable signaling wave source, is coupled through input transformer I I and leads l2 and I3 to a diode rectifier comprising diodes I4, I4 and cathode I5. Associated with the diode is a triode amplifier comprising the cathode I5, a control grid I6 and an anode l1, and with the cathode a cathode heater I8 energized by a direct current source IS. The anode circuit of the triode amplifier includes a B battery 20 and is applied through a transformer 2| to output terminals 22, 22. For the purpose of this illustration the diode-triode is a 292-A Western Electric thermionic tube. As the operation of this tube is well understood, a general description thereof will be omitted here, and only such operation as is necessary to describe the invention will be included.

In accordance with this invention a bridge network 30 has one diagonal 3|, 32 connected in series with the diode rectifier and an opposite diagonal 33, 34 connected in series with the direct current source l9 in the cathode heater circuit. Across the diagonal 3|, 32 is a capacitor 35., A variable connection 36 from one arm of the network extends to the control grid I6; The network comprises arms R1, R2+R3, R4 and R5.

In the operation of the above circuit organization, negative bias is normally provided for the control grid I6 without applying negative bias to the diodes I4, I With respect to the cathode I5. This is accomplished by maintaining R1=R2+R3, and R4=R5. Thus, with no signal input the same voltage is developed across the arms R1 and R2+R3 and also across the arms R4 and R5. Such voltage is, of course, due to a flow of current from the cathode heater source IS. The negative biasing voltage for the control grid I6 is the voltage drop across R4 minus that across R3, and may be made a suitable magnitude by adjustment of the variable connection 36.

The rectified signaling current In is independent of the ratio Rz/Rs, provided R2+R3=R1. The biasing voltage applied to the control grid I6 may be obtained by adjustment of the variable connection 36 without affecting the magnitude of the rectified current IR flowing in the lead I3. Dueto the aforementioned network arrangement the diodes I4, |4 do not receive any biasing voltage with respect to the cathode I5 as the diagonal 3|, 32 comprises equipotential points. For the purpose of this illustration, R1=2 megohms, Rz=1.2 megohms, R3=0.8 megohms, R4=l5 ohms and R5=15 ohms.

While the above description relates to a. diode and triode contained in the same envelope, it is to be understood that it is equally applicable to a diode and triode embodied in individual envelopes. The invention is not to be construed or limited to the specific details or values disclosed as these are rather for illustrative purposes, the scope being defined in the claims.

What is claimed is:

1. In a signaling wave receiver system, in combination, a source of signaling waves, a diode rectifier, circuit means to connect said diode rectifier to said wave source, an amplifier including a control grid, a cathode and a cathode heater, and a source of direct current to energize said cathode heater; means to provide for said control grid a biasing voltage which does not produce a bias in the diode circuit, comprising a bridge network having one diagonal connected in series in said circuit means in the output of said diode and the opposite diagonal in series with said cathode heater source, a capacitor connected across the one diagonal in said circuit means, and a variable connection extending from said network to said control grid.

2. In the signaling wave receiver system according to claim 1 in which said bridge network comprises equal resistance in each of two adjacent arms and other equal resistances in each of the remaining two adjacent arms.

3. In the signaling wave receiver system according to claim 1 in which the terminals of the network diagonal connected in said circuit means comprise equipotential points.

EDWARD LACEY. 

